In the prior art, the product 2-phenyl ethanol has a variety of applications. It is a colourless liquid possessing a faint but lasting odour of rose petals. Due to this 2-phenyl ethanol is important as a fragrance chemical, used in perfumes, deodorants, soaps, detergents, etc. 2-phenyl ethanol also has bacteriostatic and antifungicidal properties. Therefore, it is used in the preparation of antiseptic creams and deodorants. This alcohol is also extensively used in the formulation of various cosmetics especially in hair shampoos and hair dyes to improve the texture and the quality of hair. 2-phenyl ethanol also has local anaesthetic properties. 2-phenyl ethanol finds applications in chemical industries, for the manufacture of important chemicals such as styrene, phenyl ethyl ester, phenyl acetaldehyde, phenyl acetic acid, benzoic acid, bis-phenyl ether, etc. As it contains aromatic ring, 2-phenyl ethanol can be nitrated, sulphonated, or chlorinated to give various substituted industrially important compounds.
Conventionally, 2-phenyl ethanol is prepared by Grignard synthesis in which chlorobenzene is converted to phenylmagnesium chloride which reacts with ethylene oxide at 100.degree. C. to give phenylethoxy magnesium chloride which is then decomposed with sulphuric acid to give 2-phenyl ethanol. This process involves the use of dangerous diethyl ether as a solvent. Also it is very difficult to prepare phenyl magnesium chloride in situ. However, the main problem of this process is the quality of the 2-phenyl ethanol, which is of utmost importance in the production of perfumery chemicals. The major side product obtained is biphenyl along with amounts of rearranged side products, which cannot be separated from 2-phenyl ethanol even by vacuum distillation. [Ernst T. Theimer in Fragrance Chemistry, page 271, Academic Press, New York (1982)].
Another conventional method for the preparation of 2-phenyl ethanol involves low temperature Friedel Crafts alkylation of benzene with ethylene oxide, in the presence of anhydrous aluminium chloride. The major draw back of this process is that the temperature (i.e., below 25.degree. C.) and molar ratios of the reactants are extremely critical and it is very difficult to maintain these reaction parameters. At a slightly higher temperature coupling takes place forming a dibenzyl compound. In addition, this process is not an eco-friendly process due to the use of AlCl.sub.3 as a reagent. [Richard Wilson in Kirk Other's Encyclopaedia of Chemical Technology Vol. 4, page 116, John Wiley & Sons, New York (1991)]. 2-phenyl ethanol is also prepared via reduction of styrene oxide by using different reducing agents like LiAlH.sub.4, LiAlH.sub.4 /AlCl.sub.3, B.sub.2 H.sub.6, LiInH.sub.4, NaBH.sub.4, and LiBHEt.sub.3. The preparation of these reagents introduces an additional step in the process and the use of reagents on a commercial scale may not be feasible. Also, the use of these reagents lead to the formation of a mixture of primary and secondary alcohol. Reduction of styrene oxide with Lithium Indium hydride has been reported to give only 33% of 2-phenyl ethanol. [Koji Tanaka et. al,. Tetrahedron letters 36, 18,3169-3172, (1995)].
Catalytic hydrogenation of styrene oxide, using both homogeneous and heterogeneous catalysts have also been reported. The use of homogeneous catalysts poses a serious problem of separation and recovery of pure PEA. Various patents have made attempts to increase the selectivity of PEA using heterogeneous catalysts. Among the heterogeneous catalysts, Raney nickel was generally used alone or along with various promoters. According to U.S. Pat. No. 2,822,403, catalytic hydrogenation of styrene oxide was carried out in the presence of water. Use of emiulsifying or dispersing agents was recommended to achieve the required yield. In this process the catalyst used was a combination of Raney nickel and other hydrogenating catalyst like Cobalt, Platinum and Palladium. However, this process has several disadvantages. For instance, expensive and time consuming distillation is required to remove large amounts of water. Solvent extraction and salting out procedure are rendered difficult due to the presence of emulsifying agents. The greatest disadvantage of the process of this patent is the formation of large quantities of ethyl benzene, which destroys the aroma of PEA. British Patent No. 760.768 describes a similar catalytic hydrogenation of a suspension of styrene oxide and water. However, this patent suggests the use of Raney nickel alone instead of a combination of Raney nickel and Palladium. This process also suffers from the previously discussed disadvantages. U.S. Pat No. 3, 579,593, which is equivalent to DE 1,918,852 describes hydrogenation of styrene oxide, again using a combination of Raney nickel and Palladium. Specific metal compositions of Raney nickel and Palladium are disclosed. According to this patent, neither of the catalysts alone, gives good results. Using Raney nickel alone, 10% ethyl benzene is formed which totally destroys the aroma of PEA, while use of Palladium alone as a catalyst produces 11% acetaldehyde. Besides this, PEA formation is only 85%. In Patent No. DE 3,239,611, PEA selectivity was as high as 97% by a two step hydrogenation of styrene oxide and using a combination of acetic acid and triethyl amine as a promoter system.
Hydrogenation of styrene oxide containing &lt;0.5% chloro derivatives of styrene oxide was also carried out in a fixed bed reactor using Ni/Al.sub.2 O.sub.3 as a catalyst at hydrogen pressure &lt;2 MPa and temperature 338-353.degree. K. The resulting crude product contained 66% 2-phenyl ethanol, styrene oxide 6.7%, ethyl benzene 23.5%, toluene 1.6%. [Patent Szydlowska Tueno, Celler, Pol. PL 137,142 (1987)].
Recently, gas phase hydrogenation of styrene oxide over pentasile type zeolite phosphate doped with a metal as a catalyst to give 2-phenyl ethanol has been reported. The styrene oxide and hydrogen were passed through a tube reactor packed with catalyst prepared by calcining a borosilicate with Cu(NO.sub.3).sub.2 at 540.degree. C. to give 78.4% 2-phenyl ethanol. [Holderich Wolfgang, Goelz Narbert, Hupfer Leopold (BASF) Ger offen DE 3,801,106,(1989)].
The above-mentioned process suffers from various drawbacks such as use of hazardous chemicals, separation of the catalyst used, separation of the product and the selectivity.